Method of depositing inorganic coatings from vapour phase

ABSTRACT

A METHOD OF DEPOSITING INORGANIC COATINGS FROM VAPOUR PHASE INVOLVES THE FORMATION OF VAPOUR PHASE OF LIQUID COMPOUNDS OF ELEMENTS, AS WELL AS SOLUTIONS OR SUSPENSIONS OF VOLATILE COMPOSITONS OF SAID ELEMENTS ADAPTED TO RELEASE DEPOSITED ELEMENTTS OF COMPOSITIONS TTHEREOF DURING THERMAL DECOMPOSITION DUE TO HEATING AND VAPORIZATION OF   SAID LIQUID OVER THE ENTIRE SURFACE OF A WORKPIECE BY PROPER THERMAL RADIATION OF THE WORKPIECE BEING TREATED. TO THIS END SAID LIQUID IS SUPPLIED UNDER THE FORCE OF GRAVITY ADJACENT TO AND ALONG SAID WORKPIECE.

24 1973 G. A. DOMRACHEV ETAL 3,729,335

METHOD OF DEPOSITING INORGANIC COATINGS FROM VAPOUR PHASE Filed April 22, 1971 Patented Apr. 24, 1973 3,729,335 METHOD OF DEPOSITING INORGANIC COATINGS FROM VAPOUR PHASE Georgy Alexeevich Domrachev, ulitsa Minina 15a, kv. 3; Valery Vasilievich Melnikov, ulitsa Eltonskaya 50, kv. 3; Georgy Borisovich Kazarinov, ulitsa Belinskogo 106a, kv. 7; Gleb Alexandrovich Skorik, ulitsa Surikova 12, kv. 56; and Konstantin Konstantinovich Fukin, prospekt Lenina 30, korpus 7, kv. 61, all of Gorky,

Filed Apr. 22, 1971, Ser. No. 136,481 Claims priority, application U.S.S.R., May 29, 1970, 1,432,551 Int. Cl. B44d 1/02 US. Cl. 117-95 4 Claims ABSTRACT OF THE DISCLOSURE A method of depositing inorganic coatings from vapour phase involves the formation of vapour phase of liquid compounds of elements, as well as solutions or suspensions of volatile compositions of said elements adapted to release deposited elements or compositions thereof during thermal decomposition due to heating and vaporization of said liquid over the entire surface of a workpiece by proper thermal radiation of the workpiece being treated. To this end said liquid is supplied under the force of gravity adjacent to and along said workpiece.

The present invention relates to a method of depositing inorganic coatings from vapour phase of liquid metal or non-metal compounds onto the surface of a workpiece being treated.

Known in the prior art is a method of depositing inorganic coatings from vapour phase of liquid compounds of metals or non-metals such as silicon, germanium or boron, as well as solutions or suspensions of volatile compoitions of said elements used in combination or separately onto the urface of a workpiece being treated which is heated at the temperature corresponding to the release of deposited elements or compositions thereof from decomposable compounds.

By this method the deposition of coatings of highly volatile decomposition products is, however, non-uniform, that is the rate of deposition is initially increased with consequent decrease by a factor of as much as several hundred, the rate of deposition being limited by the mass transfer rate (diffusion rate) of a decomposed substance moving to a support or workpiece in the atmos phere, wherein the main part of the total pressure is con-.

stituted by a partial pressure of decomposition products.

An increase of the partial pressure of decomposition products results in condensation of vapour of a parent decomposable compound which precipitates over the whole volume of a deposition chamber in the form of condensed phase. In all prior art methods of depositing coatings from vapour phase this phenomenon results in a decrease of the deposition rate and reduction of the speed of formation of vapour phase from a decomposable sub stance. For this reason, in prior art methods of depositing coatings from vapour phase maximum rates of a coating growth (as to thickness) generally do not exceed 0.01- 0.02 mm. per hour.

All prior art methods of depositing coatings from vapour phase may be divided into two main groups. The first group comprises the introduction of vapour phase, which has been preliminary formed, into contact with a heated workpiece being treated, the vapour phase being insulated from condensed phase of a parent substance in equilibrium therewith, that is the deposition is taking place from non-equilibrium vapour phase. The second group involves the introduction of vapour phase into contact with a workpiece being treated, the vapour phase being in equilibrium with respect to an excess of the condensed phase of a decomposable substance, said condensed phase being disposed below said workpiece being treated.

The contact per se with non-equilibrium vapour phase presupposes a decrease of the deposition rate due to a reduction of concentration of a decomposable substance intensified by condensation of vapour thereof under high concentration of vapour of decomposition products. For this reason, high deposition rates and uniformity in composition and structure of coatings may be achieved by this method only at the initial stages of treatment.

The second of the above-mentioned prior art methods of depositing coatings from vapour phase by contacting equilibrium vapour phase with a workpiece disposed above condensed phase of a decomposable substance results in all instances in non-uniform growth of a coating due to nonuniform change of the deposition rate resulting from the formation of decomposition products and dew precipitation from condensed phase of a parent substance. As a result, a substantial reduction of content of a decomposed substance in vapour phase occurs which is intensified both by the force of gravity acting on condensate particles formed from a parent decomposable substance, which is directed from a support (workpiece) downwards to an excess of condensed phase, and by thermal diffusion, since the temperature at a point adjacent to the support is higher than that in the vicinity of the condensed phase disposed below the workpiece. These factors result in a reduction of the deposition rate and in non-uniformity of a coating in thickness and chemical composition, which in a number of cases is manifested by laminar structure of films, as well as by a great difference between the thickness of the film at the upper and lower portions of a sample in the case of elongated workpieces.

It is an object of the present invention to overcome the above difficulties.

It is the main object of the present invention to provide a method of depositing inorganic coatings from vapour phase onto the surface of workpieces which will allow the acceleration of the formation of a coating on a workpiece and the obtaining of uniform thickness of a coating having homogenous chemical composition.

The above object is accomplished by a method of depositing inorganic coatings from vapour phase of liquid compounds of metals and non-metals such as silicon, germainium or boron, as well as solutions and suspensions of volatile compositions of said elements used in combination or separately onto the surface of a workpiece being treated, the workpiece being heated at the temperature corresponding to the release of deposited elements or compositions thereof from decomposable compounds, wherein, according to the present invention, said decomposable liquid is supplied under the force of gravity over the surface of said workpiece being coated at a distance ensuring heating and vaporization of decomposable compounds under the action of thermal radiation of said workpiece, as well as creation of vapour phase over the entire surface of said workpiece being treated.

Th s method permits a substantial increase in the rate of deposition of inorganic coatings from vapour phase and an improvement of the uniformity of thickness thereof, as well as homogeneity in chemical composition.

It is advantageous to supply a decomposable liquid upon a guide surface preferably disposed equidistantly with respect to the surface of a workpiece being treated.

The present method results in an improvement in homogeneity and uniformity of coating on the surface of workpieces having complicated shapes.

The guide surface to receive a decomposable liquid may comprise the surface of a cylindrical rod adapted to be introduced into the interior of a workpiece.

The present method results in an improvement in homogeneity and uniformity of coating deposited upon the mternal surface of elongated tubular workpieces.

The invention will be better understood from the following description of one embodiment of a method of depositing inorganic coatings from vapour phase with reference to the accompanying drawing, which is an elevational view partly in section of a tubular workpiece with a rod.

The method according to the present invention is performed in the following way:

A rod 2 is introduced into the interior of a workpiece 1 to supply a liquid from a tube 3 therealong, said liquid containing elements necessary to form an inorganic coating on the surface of the workpiece 1 being treated.

Liquid compounds of metals and non-metals such as silicon, germanium or boron, may be used, as well as solutions or suspensions of volatile compositions of said elements taken in combination or separately.

For example, in the method according to the invention there may be employed hydrides, mixed hydrides, halogenides, alcoholates, fl-diketonates, alkyl and aryl compounds of metals and non-metals such as silicon, germanium and boron, sandwich-compounds of transition metals of the group of bis-aren metal, bis-cyclopentadienyl metal, metal carbonyls, mixed sandwich carbonyls and nitrosyls of metals, etc. Some chemical compounds may be obtained in the liquid state by melting a compound, the melt being used in particular in case of fusible substances.

As solutions of compounds in the method according to the invention may be employed solutions of solid, liquid and gaseous compounds, high-boiling liquids which are not decomposable under conditions of deposition of coatings and are adapted form during thermal decomposition readily removable and volatile products being preferably used as solvents. As an example of such solvents hydrocarbons such as tetralin, Decalin, diphenylmethane homologues, etc., halogen derivatives of hydrocarbons such as chloronaphthalenes, chlorodiphenyls, etc., ethers and esters such as dimethyl esters of di-, triand polyethylene glycol, dialkylphthalates and so on. Compounds to be used for deposition of coatings according to the method of the invention by employment of solutions thereof must be sufiiciently soluble to prepare solutions and to volatilize these compounds during the heating for creation of vapour phase at the deposition stage. Compounds to be used in the form of solutions may be of one of the classes mentioned above but without limitation as to state of aggregation.

As suspensions of compounds in the method according to the invention may be used suspensions of solid volatile compounds of the classes referred to above in liquids which are not decomposable under conditions of deposition of coatings or which are decomposable with formation of readily removable thermal decomposition products similarly to the above-mentioned solutions. For preparation of suspensions the same liquids may be used as described above with reference to preparation of solvents.

In the method according to the invention decomposable liquids may be used both separately and in combinations in dependence of composition of a coating to be deposited.

The method according to the invention may be carried out in an appropriate deposition chamber provided with the decomposable liquid input and the deposition products output, the chamber having to accommodate a workpiece heated at desired temperature before deposition. A workpiece may be heated by any method such as resistive heating, inductive heating, radiation, etc. The method according to the invention may be performed either at reduced pressure or in the atmosphere of an inert gas or a reaction reduction or oxidation gas, etc.

In the exampl s gi en hereinb low the method accordposable liquid supply into the deposition chamber, characteristics of a coating produced and the rate of deposition thereof.

EXAMPLE I Decomposable liquid-chromium (O) bis-ethyl-benzene.

Sample--graphite cylinder with an internal diameter of 20 mm., an external diameter of 40 mm. and a height of 60 mm., the internal surface of the cylinder being coated.

Guide surface the cylindrical surface of a rod of 4 mm. diameter axially arranged within the sample.

The temperature of the sample-450 C. (inductive heating).

The initial pressure5-1()- mm. of mercury.

The rate of the decomposable liquid supplyml. per hour.

Characteristics of the coatingwithin 1 hour chromium coating homogenous in composition and uniform in thickness was produced with a thickness of 1.1 mm. having fine and brilliant metallic surface and high hardness and adherence to the support.

The deposition rate was of 1.1 mm. per hour.

EXAMPLE 2 Decomposable liquid-chromium (O) bis-ethyl-benzene.

Sample-the same as described in Example 1.

Guide surface-the same as described in Example 1.

The temperature of the sample450 C.

The initial pressure5-10 mm. of mercury. The rate of the decomposable liquid supply-50 ml. per hour. Characteristics of the coating-within 1 hour the coatmg similar to that produced in Example 1 was obtained but having a thickness of 0.3 mm.

The deposition rate was 0.3 mm. per hour.

EXAMPLE 3 Decomposable liquid-chromium (O) bis-ethyl-benzene.

Samplethe same as described in Example 1.

Guide surface-the same as described in Example 1.

The temperature of the same450 C.

The initial pressure-5 10- mm. of mercury.

The rate of the decomposable liquid supply-200 ml. per hour.

Characteristics of the coating-within 1 hour the coating similar to that produced in Example 1 was obtained, but having a thickness of 1.8 mm.

The deposition rate was of 1.8 mm. per hour.

EXAMPLE 4 Characteristics of the coatingwithin hours the metallic chromium was produced which weighed 70 g. when removed from the aluminium sample.

EXAMPLE 5 The deposition rate was 14 g. per hour.

Decomposable liquid-chromium (O) bis-cumene.

Samplea steel cone with a base diameter of 60 mm. and a height of 60 mm., the external surface being coated.

Guide surfacethe internal surface of a rotatable metallic conical funnel disposed at 20 mm. above the cone to be coated and enclosing the whole cone (the diameter of the funnel base was 100' mm.).

The temperature of the sample-400 C. (the internal resistive heating of the cone).

The initial pressure--1-10- mm. of mercury.

The rate of the decomposable liquid supply-100 ml. per hour.

Characteristics of the coatingwithin half an hour uniform and brilliant chromium layer was produced over the whole surface of the cone having a thickness of 0.4 mm.

The deposition rate was .08 mm. per hour.

EXAMPLE 6 Decomposable liquidchromium (O) bis-cumene.

Samplea steel plate 50 mm. X 100 mm. with a thickness of 4 mm.

Guide surface-the surface of a plate having the same dimensions as that being coated which was obliquely positioned, as well as the plate being coated (at 30 with respect to a vertical) and at 20 mm. above the sample.

The temperature of the sample400 C. (resistive heating).

The initial pressure---2-10 mm. of mercury.

The rate of the decomposable liquid supp1y-50 ml. per hour.

Characteristics of the coating--within half an hour brilliant chromium coating was produced on one side of the plate with a thickness of 0.1 mm.

The deposition rate was 0.2 mm. per hour.

EXAMPLE 7 Decomposable liquid-molybdenum (O) bis-ethyl-benzene.

Samplea glass cylinder of 40 mm. diameter and with a height of 50 mm.

Guide surface-a glass rod with cylindrical surface of 5 mm. diameter coaxially disposed within the sample.

The temperature of the sample380 C. (resistive heating by means of a heater).

The initial pressure---1-10 mm. of mercury.

The rate of the decomposable liquid supply-100 ml.

. per hour.

Characteristics of the coatingwithin half an hour molybdenum coating was produced having a thickness of 0.4 mm. with even and brilliant surface having good adherence to the glass support.

The deposition rate was 0.8 mm. per hour.

EXAMPLE 8 EXAMPLE 9 Decomposable liquid-nickel-cyclopentadienyl-nitrosyl. Samplea ceramic cylinder have an internal diameter EXAMPLE 10 Decomposable liquidnickel bis isopropylcyclopentadienyl.

Samplethe same as described in Example 9.

Guide surface-the same as described in Example 9.

The temperature of the sample400 C.

The initial pressure---5-10 mm. of mercury.

The rate of the decomposable liquid supply-1.0 ml. per minute.

Chacteristics of the coating-similar to that produced in Example 9.

The deposition ratel1.0 micrometers per minute.

EXAMPLE ll Decomposable liquidzirconium-tetrakis-borohydride.

Samplethe same as described in Example 1.

Guide surfacethe same as described in Example 1.

The temperature of the sample400 C. (inductive heating).

The initial pressure-140* mm. of mercury.

The rate of the decomposable liquid supply-50 ml. per hour.

Characteristics of the coating-uniform hard coating of zirconium in a mixture with zirconium boride was produced.

The deposition rate was 0.4 mm. per hour.

Example 12 Decomposable liquid--trimethylaluminium.

Samplethe same as described in Example 6.

Guide surface--the same as described in Example 6.

The temperature of the sample350 C.

The initial pressure1-10- mm. of mercury.

The rate of the decomposable liquid supply 50 ml. per hour.

Characteristics of the coating-within 5 hours a coating with a thickness of 1.0 mm. was produced having a composition corresponding to aluminium carbide.

The rate of deposition was 0.2 mm. per hour.

EXAMPLE 13 Decomposable liquid-tetraisoamylgermanium.

Samplea sitall plate with the dimensions as indicated in Example 6.

Guide surface-the same as described in Example 6.

The temperature of the sample---l-l0 mm. of mercury.

The rate of the decomposable liquid supplyml. per hour.

Characteristics of the coating-within half an hour brilliant germanium coating was produced with a thickness of 0.2 mm.

The deposition rate was 0.4 mm. per hour.

EXAMPLE 14 Decomposable liquidtributylantimony.

Samplethe same as described in Example 13. Guide surfacethe same as described in Example 13. The temperature of the sample350 C.

The initial pressure1-10- mm. of mercury.

The rate of the decomposable liquid supplySO ml. per hour.

Characteristics of the coatin-gwithin half an hour brilliant gray crystalline antimony coating was produced with a thickness of 0.15 mm.

The deposition rate was 0.3 mm. per hour.

EXAMPLE Decomposable liquidtetraethoxysilane.

Samplea cylinder of Kovar alloy with an internal diameter of mm. an external diameter of 23 mm. and a height of 50 mm.

Guide surfacethe same as described in Example 9.

The temperature of the sample-600 C. (inductive heating).

The initial pressure-760 mm. of mercury.

The rate of the decomposable liquid supply0.3 ml. per minute.

Characteristics of the coating-glassy layer consisting of silicon dioxide deposited on the internal surface of the sample with a thickness of micrometer.

The deposition rate was 1.0 micrometer per minute.

EXAMPLE 16 Decomposable liquidtetrabutyltitanate.

Samplea sitall plate with a diameter 20 mm. and a thickness of 2 mm. coated with thin aluminium film.

Guide surfacethe surface of a rotatable inverted cone with a base diameter of 30 mm. disposed at 10 mm. above the sample.

The rate of the decomposable liquid supply was of 0.5 ml. per minute.

Characteristics of the coatingcontinuous dark coating having a specific resistance of 82 ohm per cm. and consisting of a mixture of rutile and anatase.

The temperature of the sample-450 C.

The initial pressure2- 14* mm. of mercury.

The deposition rate was 1.5 micrometers per minute.

EXAMPLE 17 Decomposable liquidtris-secondary butylato-alumini- Samplea bar of Kovar alloy with a diameter of 20 mm., a length of 50 mm.

Guide surfacea coil of nickel band (3 mm. width) with a coiling diameter of mm. and a pitch of 15 mm., the coil enclosing the sample coaxially therewith.

The temperature of the sample-500 C.

The initial pressure2 10* mm. of mercury.

The rate of the decomposable liquid supply-0.5 ml. per minute.

Characteristics of the coatingcolourless continuous glassy coating with a composition corresponding to aluminium oxide.

The deposition rate was 1.7 micrometers per minute.

EXAMPLE 18 Decomposable liquida melt of aluminium triisopropylate.

Sample and all the remaining conditionsthe same as described in Example 17. v

The decomposition rate was 2.1 micrometers per minute.

EXAMPLE 19 Decomposable liquid-triamylborate.

Samplethe same as described in Example 16.

Guide surfacethe same as described in Example 16.

The temperature of the sample500 C.

The initial pressure-760 mm. of mercury.

The rate of the decomposable liquid supply1.0 ml. per minute.

Characteristics of the coating-transparent glassy layer having a composition corresponding to boric acid anhydride.

The decomposition rate was of 7.0 micrometers per minute.

8 EXAMPLE 20 Decomposable liquid-germanium tetrachloride.

Sample-the same as described in Example 13.

Guide surfacethe same as described in Example 13.

The temperature of the sample850 C.

The initial pressure of the hydrogen atmosphere-760 mm. of mercury.

The rate of the decomposable liquid supply50 ml. per hour.

Characteristics of the coating-brilliant crystalline layer of germanium.

The deposition rate was 0.6 micrometer per hour.

EXAMPLE 21 Decomposable liquida mixture of mol percent cyclopentadienyl nitrosyl nickel and 20 mol percent chromium (O) bis-ethyl-benzene.

Samplea ceramic cylinder of 20 mm. internal diameter, 26 mm. external diameter and a height of 50 mm.

Guide surface-a tube made of a fine nickel wire network, the tube with a diameter of 4 mm. being coaxially disposed within the sample.

The temperature of the sample-400 C.

The initial pressure5- 10 mm. of mercury.

The rate of the decomposable liquid supply-1.3 ml. per minute.

Characteristics of the coatingbrilliant metallic coating having a composition corresponding to Nichrome.

The decomposition rate was 15 micrometers per minute.

EXAMPLE 22 Decomposable liquid-an equimolecular mixture of tributylindium and tributylantimony.

Samplethe same as described in Example 13.

Guide surfacethe same as described in Example 13.

The temperature of the sample-450 C.

The initial pressure5-10 mm. of mercury.

The rate of the decomposable liquid supply0.6 ml. per minute.

Characteristics of the coatingdark-c0lour layer with metallic lustre having a composition corresponding to indium antimonide.

The decomposition rate was 7.0 micrometers per minute.

EXAMPLE 23 Decomposable liquidan equimolecular mixture of triethylgallium and triethylarsine.

Samplea vertically positioned sapphire plate of 20 mm. diameter with a thickness of 1 mm.

Guide surfacea vertically positioned flat network parallel with the sample surface spaced at a distance of 15 mm. from the latter.

The temperature of the sample450 C.

The initial pressure-1 10' mm. of mercury.

The rate of the decomposable liquid supply0.6 ml. per minute.

Characteristics of the coating-coating with metallic lustre having a composition corresponding to gallium arsenide.

The deposition rate was 6.0 micrometers per minute.

EXAMPLE 24 Decomposable liquida mixture of 25 mol percent tetrabutoxysilane and 75 mol percent tris-secondary butylatoaluminium.

Samplethe same as described in Example 17.

Guide surface-the same as described in Example 17.

The temperature of the sample-550 C.

The initial pressure5'10 mm. of mercury.

The rate of the decomposable liquid supply0.6 ml. per minute.

Characteristics of the coating-glassy layer having a composition corresponding to the presence of silicon dioxide and aluminium dioxide in the ratio of 1:3.

The deposition rate was 1.6 micrometers per minute.

EXAMPLE 2s Decomposable liquid-solution of bis-allylpalladiumchloride in chloronaphthalene.

Sample-a glasstextolite cylinder with dimensions as indicated in Example 7.

Guide surface-the same as described in Example 7.

The temperature of the sample-240 C.

The initial pressure-1-l'0- mm. of mercury.

The rate of the decomposable liquid supply depends on concentration of a solution and should provide for the supply of 1.0 g. per minute of solid bis-allylpalladiumchloride.

Characteristics of the catingbrilliant palladium layer on the internal surface of the sample having good adherence to the support and electric conductivity corresponding to that of pure palladium.

The deposition rate was 7 micrometers per minute.

EXAMPLE 26 Decomposable liquid-solution of bis-allylpalladiumchloride in dichlorobenzene.

Sample-a fluoroplastic plate with dimensions as indicated in Example 6.

Guide surface-the same as described in Example 6.

The temperature of the sample-250 C.

The initial pressure1-10- mm. of mercury.

The rate of the decomposable compound supply0.5 g. per minute.

Characteristics of the coating--uniform continuous brilliant palladium layer having good adherence.

EXAMPLE 27 Decomposbale liquid-solution of tungsten hexacarbonyl in tetralin.

Samplethe same as described in Example 1.

Guide surface-the same as described in Example 1.

The temperature of the sample600 C.

The initial pressure-J60 mm. of mercury.

The rate of the decomposable compound supply100 g. per hour.

Characteristics of the coating-within 1 hour tungsten coating with a thickness of 0.8 mm. was produced having good adherence to the support and brilliant surface.

The deposition rate was 0.8 mm. per hour.

EXAMPLE 28 Decomposable liquid-bis hexafluoracetylacetonatocopper in a tetralin solution saturated with hydrazine.

Sample-the same as described in Example 7.

Guide surfacethe same as described in Example 7.

The temperature of the sample-380 C.

The initial pressure-760 mm. of mercury.

The rate of the decomposable compound supply-50 g. per hour.

Characteristics of the coating-brilliant crystalline copper layer on the internal surface of the sample having good adherence.

The deposition rate was 15 micrometers per minute.

EXAMPLE 29 Decomposable liquid-a suspension of dibenzenechromium in tetralin.

Samplethe same as described in Example 1.

Guide surface-the same as described in Example 1.

The temperature of the sample400 C.

The initial pressure-1-10- mm. of mercury.

The rate of the decomposable compound supply-l00 g. per hour.

Characteristics of the coating-the same as indicated in Example 1, a thickness of 0.9 mm.

The deposition rate was of 0.9 mm. per hour.

EXAMPLE 30 Decomposable liquid-a suspension of copper formiate in tetralin.

Sample and all the remaining conditionsthe same as described in Example 28.

The deposition rate was 12 micrometer per minute.

EXAMPLE 31 Decomposable liquid--a suspension of bis-cyclopentadienylcarbonylnickel in tetralin.

Sample and all the remaining conditionsthe same as described in Example 9.

The rate of decomposable compound supply-1.2 g. per minute.

Characteristics of the coating-brilliant nickel layer with good adherence.

The deposition rate was of 9 micrometers per minute.

EXAMPLE 32 Decomposable liquida suspension of a mixture of 20 mol percent dibenzenechromium and mol percent bis-cyclopentadienylcarbonylnickel in dimethylester of diethylene glycol.

Sample and all the remaining conditionsthe same as described in Example 21.

The rate of the decomposable mixture supply-4.0 g. per minute.

Characteristics of the coating-brilliant metallic layer having electric conductivity corresponding to that of Nichrome.

The deposition rate was 7 micrometers per minute.

EXAMPLE 33 Decomposable liquid-a suspension of dibenzenechromium in cyclopentadienylnitrosylnickel in the ratio of 1:4.

Sample and all the remaining conditionsthe same as described in Example 21.

The deposition rate was 13 micrometers per minute. The workpiece is heated at the temperature corresponding to the release of deposited elements or compositions thereof from decomposable compouds. The liquid supplied through the tube 3 fiows under the gravity over the surface of the rod 2, said liquid being heated and vaporized. The distance between the surface of the rod 2 and the surface of the workpiece 1 being treated should be such as to ensure heating and vaporization of decomposable compounds under the action of thermal radiation of said workpiece, as well as creation of vapour phase over the entire surface of the workpiece being treated. The guide surface for a decomposable liquid is preferably disposed equidistantly with respect to the surface of the workpiece being coated over the whole area thereof.

The formation or deposition of a coating on the surface of a workpiece is taking place with continuous flow of a liquid along the surface being treated. Due to vaporization of a liquid under the action of thermal radiation of the workpiece, the concentration of vapour of a parent substance will be in equilibrium with respect to condensed phase thereof. As the liquid flows over the surface of the workpiece being coated, it is being heated up to higher temperatures thus providing for more intensive vaporization of a decomposable substance which contributes to an increase of the content thereof in vapour phase and, hence, to an increase of the rate of coating deposition. An increase of concentration of a decomposable substance vapour will be also promoted by the fact that particles of condensed phase, which have been formed upon the increase of the decomposition products pressure, are moved under the force of gravity over the surface of a workpiece being coated, heated and revaporized.

Accordingly, saturated vapor is in equilibrium with respect to a decomposed liquid along the whole flow path thereof.

All the above factors result in considerable increase of concentration of vapour phase during the deposition of coating and ensure high deposition rates, as well as the formation of coatings which are more uniform in thickness and chemical composition due to smaller relative fluctuations of concentration of a decomposed substance and decomposition products respectively, while retaining high absolute value of concentration of a decomposable substance.

During the tests of the method according to the present invention the deposition rates of the order of 1-2 mm. per hour were achieved which was as much as 100 times higher as compared to ordinary rates of deposition from vapour phase by prior art methods. The coatings thus formed were more homogeneous in chemical composition and uniform in thickness than those produced during long deposition for many hours for obtaining coatings of the same thickness by prior art methods.

The method according to the present invention permits the depositing of coatings of metals, oxides and other materials onto different supports.

This method is the most eflicient in producing coatings having complicated shapes, such as cylinders, rings, tubes upon the external and internal surfaces of workpieces having complicated shapes, such as cylinders, rings, tubes and spheres.

For coating the internal surface of graphite or metal samples of cylindrical shape (external diameter 70 mm., internal diameter 30 mm., height 50 mm.) as a guide surfac was used the surface of a metal or glass cylindrical rod of 3-4 mm. diameter disposed along the axis of a cylindrical sample. The above-mentioned samples were coated with chromium with metered supply of a liquid organic compound of chromiumchromium bis-ethylbenzene (o)directly into a vacuum deposition chamber onto the surface of the vertically positioned guide rod. The process was performed in vacuum at 3-10 -2-10 mm. of mercury and at the temperature of heating of a sample being coated of 400 C. Upon conditioning the sample to said temperature and pressure chromium bisethylbenzene was supplied into the chamber for deposition at the speed of 0.3-0.5 ml. per minute. In this case, under constant evacuation of decomposition products at the rate of 0.5-2.1 per second, the deposition rate achieved up to -21 microns per minute, and within 60-90 minutes the coating with a thickness of 1.5-2.0 mm. was obtained. The method has been also tested in depositing dielectric coatings of silcia and aluminium oxide when tetraethoxysilane and tri-secondary butyloxyaluminium respectively were subject to thermal decomposition.

The method according to the invention allows the deposit of coatings of metals, dielectrics and other materials which are uniform in thickness and homogeneous in composition onto workpieces and parts.

What is claimed is:

1. A method of depositing inorganic coatings from a vapour phase of liquid metal or non-metal compounds onto the surface of a workpiece being treated comprising the steps of heating the workpiece at a temperature corresponding to the evolution of deposited elements or compositions thereof onto the surface of said workpiece from volatile decomposable compounds of metals or non-metals such as silicon; germanium, and boron; supplying by gravity a decomposable liquid comprising said liquid compounds of metals or non-metals, solutions or suspensions of said volatile compounds employed either separately or in combination along the surface being coated of said workpiece starting at the top portion of said workpiece at a distance ensuring heating and vaporization of said decomposable compounds and formation of a vapour phase over the whole area in the proximity to the surface of said workpiece under the influence of thermal radiation from said heated workpiece.

2. A method of depositing inorganic coating from a vapour phase of liquid metal or non-metal compounds onto the surface of a workpiece being treated comprising the steps of heating of the workpiece to a temperature corresponding to the evolution of deposited elements or compositions thereof onto the surface of said workpiece from volatile decomposable compounds of metals or non-metals such as silicon, germanium, and boron; supplying by gravity a decomposable liquid comprising said liquid compounds of metals or non-metals, solutions or suspensions of said volatile compounds employed either separately or in combination, alongside the surface of said workpiece starting from the top portion of said workpiece over a guiding surface from its uppermost point, said guiding surface being spaced from the surface of said workpiece at a distance ensuring heating and vaporization of said decomposable compounds under the influence of thermal radiation from said heated workpiece and the formation of a vapour phase over the whole area in the proximity to the surface of said workpiece.

3. A method as claimed in claim 2, wherein said guiding surface is spaced equidistantly from the surface of said workpiece.

4. A method of depositing inorganic coating from a vapour phase of liquid metal or non-metal compounds onto the surface of a workpiece being treated comprising the steps of heating said workpiece to a temperature corresponding to the evolution of deposited elements or compositions thereof onto the surface of said workpiece from volatile decomposable compounds of metals or non-metals such as silicon, germanium, and boron; supplying by gravity a decomposable liquid comprising said liquid compounds of metals or non-metals, solutions or suspensions of said volatile compounds employed either separately or in combination alongside the inner surface to be coated of said workpiece along a guiding surface from the uppermost point thereof, said guiding surface comprising a cylindrical rod surface inserted inside said workpiece; said guiding surface being equidistantly spacedfrom the surface of said workpiece being coated, thereby ensuring heating and vaporization of said decomposable compounds under the influence of thermal radiation from said heated workpiece and formation of a vapour phase over the whole area in the proximity to the inner surface of said workpiece.

References Cited UNITED STATES PATENTS 3,565,676 2/1971 Holzl ll7-107.2 R 3,375,129 3/1968 Carley et al. ll7l97.2 R 2,700,365 11/1955 Pawlyk 1l7107.2 R 2,767,464 10/1956 Nack et al ll795 X EDWARD G. WHITBY, Primary Examiner U.S. Cl. X.R.

1l794, 97, 106 A, 107.2 R, 131 

